The present invention relates to a thin-walled rubber article, such as for instance gloves or condoms, prepared by dip forming. Morever, the invention relates to a process for the preparation of such rubber article and to a solution for the preparation of said rubber article.
Soft, elastomeric, protective rubber articles, for instance gloves or condoms, have for a long time been made from natural latex or natural rubber dissolved in a suitable solvent, for instance aliphatic hydrocarbons. In order to obtain articles with a sufficiently high strength and elasticity it is necessary to vulcanize or in other ways chemically cross-linking the molecule chains of the rubber, which requires the presence of curing-agents, activators, accelerators, and possibly antioxidants. The presence of such agents often give rise to allergic reactions among the users of said articles.
Furthermore, all latices of natural rubber contains proteins, which may cause type I allergy (immediate hypersensitivity reaction) resulting in fatal cases in anaphylactic chock.
Great efforts have therefore been made to develop rubber articles based on synthetically manufactured rubber types, which do not have the drawbacks of natural rubber.
Thus U.S. Pat. Nos. 3,933,723 and 5,112,900 both relate to solutions containing thermoplastic styrene-triblock copolymers and a plasticizer for the production of rubber articles. Common to the solutions disclosed in the two above-mentioned patents is that by the formation of the solid film a physical cross-linking takes place between the block copolymer molecules present in the solution, when the solvent evaporates, said cross-linking being caused by the styrene domaines of the molecular chains. Thereby the use of potentially allergy causing chemicals for the provision of a chemical cross-linking between the block copolymer molecules is avoided. Furthermore, these solutions do not contain the proteins present in natural rubber, and it is thus possible by using these solutions to prepare hypo-allergenic rubber articles.
The rubber articles disclosed in U.S. Pat. No. 3,933,723 have in comparison with the rubber articles according to U.S. Pat. No. 5,112,900 a higher tensile strength and elongation, in particular after radiation sterilization. Furthermore, they have a lower modulus and consequently a better tactility for the user. However, the tear resistance of the rubber articles disclosed in U.S. Pat. No. 3,933,723 is low, and it is desirable to improve this property in such a way that for instance a glove gets a higher mechanical stability when getting in contact with pointed articles.
The rubber articles disclosed in both the above-mentioned U.S. patents contain in order to attain the desired mechanical properties comparatively large amounts of plasticizer, which is preferably consistuted by a naphthenic or aromatic mineral oil.